A 'more objective' take on audiophile topics among other thoughts...
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Monday, 15 April 2013

MEASUREMENTS: USB Cables for Audio DACs. [2013-06-18 UPDATE]

Up to this point, as you've seen in my measurements, I have been using standard generic shielded cables for analogue and digital. As you likely also know - if you've been involved in "high end" audio for awhile - there are few issues as contentious as whether expensive cables are necessary or if they even make a difference!

I've generally steered clear of this "debate" over the years because inevitably, these discussions with friends or forum threads on-line almost never really "go" anywhere... Nobody leaves the discussion having really learned anything, and ultimately if the discussion turns into an argument, everyone just ends up feeling "pissed off".

The conclusion one usually can get agreement on is that the best cable is no cable. Cables are passive "components", and ideally should transmit signal without loss, and does not impart any kind of signature on the quality of the signal. This certainly makes sense especially in the analogue domain where noise can easily creep in, causing various distortions or raising the noise floor. But what of digital cables? When something as ubiquitous as a generic USB cable can easily transmit >20MB/sec data to a USB hard drive, how problematic can it be to get 150KB/sec across for 16/44, ~500KB/sec for 24/96 audio, or 'just' ~1.12MB/sec for 24/192 high-resolution audio!?

After all these months of testing and posting on various topics, I figure it's at least reasonable to explore the cable issue as best I can with (admittedly) the limited selection of choices I have available around here.

For the record, up to this point in time, the most expensive USB cable I have tried has been the AudioQuest Carbon (~$160 for 5') more than a year ago connected between the PC and a Benchmark DAC1 USB. I have since sold off both items. I could not clearly hear a difference with the AQ Carbon, but then again since the DAC1 uses ASRC, I really wasn't expecting much either. Since then, I've been satisfied with the selection of generic cables I've collected over the years as computer parts or 'freebies'. It is in this light that I selected among my assortment, 3 A/B USB 2.0 cables to test out:

As you can see, Cable C was made by Dr. Frankenstein. It's unreasonably long (USB specs indicate a reasonable limit at ~16'), has 2 detachable connections in between, is not even gold plated, and who knows what kind of shielding is in that thing. Furthermore, the Logitech extender portion has the thinnest wire of all the cables. Any card-carrying "audiophile" would be laughed out of town for even suggesting they use something like this!

I. Cables tested with Asynchronous USB 2.0 CM6631A interface:

Let us start with what has been previously demonstrated to be a very robust asynchronous USB interface; the CM6631A. Remember that the previous tests showed that despite different laptops used, the analogue and jitter spectra were almost identical.

II. Cables tested with Adaptive Isochronous USB 1 AUNE X1 interface:

As shown previously, this interface can get noisy if I play and record with the Aspire laptop (see the laptop post). Therefore I'm going to use my ASUS Taichi to play the test audio while measuring with the Aspire as usual.

Well, the adaptive USB interface is noisier and more jittery than the asynchronous setup as we have seen before in previous posts. Depending on which cable, we can see noise showing up at certain frequencies. For example, there's a -120dB 11.7kHz spike on Cable A, 11.3kHz for Cable B, 10kHz for Cable C. But these are not the symmetrical sidebands associated with data jitter. In fact, the low-frequency jitter associated with widening of the base around the 11kHz signal looks essentially identical and perhaps most importantly, there's really nothing unusual here to suggest that Cable C is of unusual length and construction!

For the sake of completeness, I decided to run these same "cables" through to the direct asynchronous USB 2.0 interface of the TEAC UD-501 DAC to see if we can see any differences. Some folks asked if I could try a "name brand" cable for point of reference... Suggestions included the AudioQuest Diamond, maybe some Crystal Cables... Well, I search high and low... And here's the Belkin Gold 6-ft (1.8m) which I managed to get on sale for <$10 locally :-)

That red stuff is just some electrical tape I put on it for identification on another project.

Here's the RightMark data for 24/96:

Frequency Response:

THD:

Stereo Crosstalk:

No difference.

Dunn Jitter Tests (16-bit & 24-bit tests):Belkin Gold (6'):

Cable A (3'):

Cable B (6'):

Cable C (17' monstrosity):

As you can see, the jitter plots for the TEAC are quite clean. On the whole, the 24-bit noise floor is measurably lower than the AUNE X1 but the jitter plot does show a few more noise spikes (made more obvious because of that low noise floor). This is really quite academic because we're talking about noise down near -140dB!

No evidence of significant jitter differences between the Belkin Gold or any of the other cables including that terrible looking Cable C (17-footer).

Conclusion:

No evidence in these tests to suggest that the different USB cables used here with the asynchronous CM6631A USB-to-SPDIF converter, direct asynchronous TEAC UD-501 USB DAC, or adaptive isochronous USB setups should sound different (even though one would expect Cable C to be the worst). Subjectively, listening to music with Cable C through Sennheiser HD800's sounded fine.

No evidence with the J-Test to suggest data-correlated jitter is significantly different between cables. By the way, for a good demonstration of how jitter improves with interface/cable change, look at my post on Transporter-to-Behringer connection with TosLink vs. AES/EBU. Also, remember that my Oppo BDP-105 tests were done with a single 15' USB cable - still better than Cable C in construction :-).

As usual, feel free to drop me a note if there's good data or controlled tests to suggest USB cables make a significant difference contrary to these findings.

22 comments:

Hi,I needed to use a 5 metre USB cable to hook up my PC to my DAC and was worried that it may affect the sound adversely due to it's length and inexpensive nature - £2-14p ! Now I won't worry - Thanks.Alex.

Very nice test. Still believers wil believe. Life and let life. I believe in some cable differences but not hdmi or USB. Still bought a Audioquest Forest today to supplement my Ixos hdmi cables and to serve as a powercord for my Chromecast. It may not matter but it gives me pleasure none the less.

Sorry what belatedly comment on: whether you know the most important source of which is done playing music and I suggest you mac mini that should I have a minimum of 8 GB of RAM that the processor quad core i7 and a short USB cable -pomak sound is drastically -how you bought the more expensive dac and changed most of the components in the system, that we are rehearsing in many ways and with more Compjuter laptops and operating systems defined to corist the new Mac os x and this is what you've said above, I do not forget, always use a licensed Audirvanu plus or Amarra but I suggest you Audiorvanu

So couple days ago I bought "QED Performance Graphite USB A-B Cable". The reason was to connect my DAC system to my laptop. Every time I plug that USB cable to my laptop, "Windows" operation system gives me an error message: "Power surge on hub port". So I borrowed a cheap (<2£) cable from a friend and it seems that his cable works just fine. Well I noticed couple differences:The price;The cable gauge;The ferrite core that is not present on QED cable.Could the ferrite core be a reason why this cable not working (causing a power surge)?

If there were a measurable difference between a $20 cable and a $400 cable, the ultra-expensive manufacturers would be posting their testing results and there would be no debate. But they don't do that. Why?

Read a LOT of bits-is-bits stuff and finally bought a $5 Belkin (1m) to replace the $50 Cardas (2m) I had been using. I also moved the DAC from the floor under the desk (where the viper's nest of wires and power strips sit) to the desk itself, about 2 feet from the computer. The difference was like being on a plane with noise-cancelling headphones and without. I attributed it to the isolation, and even took the Cardas to work to use on my little Audioengine 2 system. After a week I couldn't stand the Belkin. It delivered headache after headache, and I cut my sessions short despite the initial impression it made of better bass and a more balanced presentation. I then tried a DH Labs Silversonic for 70 bucks and the headaches went away and even 70-year-old recordings started sounding a bit more natural, with maybe a little more sparkle in the high end and the right amount of bass instead of a bit too much. I'm still not completely satisfied with USB audio over a dedicated CD transport, but I'm having more fun and less misery listening to tunes with the new cable, and I'm listening much longer, which equals even more fun. If I'm deluded I don't give a rat's ass... it's 70 bucks. Burgers and beer for my wife and me in a Jersey dive that we'll regret the rest of the night, while the Silversonic will keep on giving until I get tired of the sparkle and desire some Cardas mid-bass emphasis with the rolled-off top end. Vive la difference. Yes, the differences are subtle, but when you live with them for a while, they become as unlivable as a bad marriage.

In order to connect an Android phone to a standard USB device, you need to use a micro USB to USB Type A Female convertor, but this should also be an OTG Cable . A mini USB OTG cable is available in the market for affordable price.

It is very clear that you really know much about cables. I admire the fact that you have written this post from a point of information and this makes your post to be quite objective. Feel free to click on this link: Reliable Help with Speech Presentation Writing

Interesting but I hear clear differences in USB cables between my Win7 PC and North Star Design DAC. My friend using a Micromega DAC concurs with my opinions too independently. I would recommend testing a Kimber USB cable. Inexpensive and definitely different on the low end. When I sat thru a demo with a rep of Audioquest of 4 of their USB cables I was blown away; hated that the $700 cable sounded so much better but I would not expect any differences from the low end cables you tested. I ended up with an $89 Furutech USB cable. Just the most transparent of the few I tried. Basically which measurements relate to low level detail, ambiance, and reverb trails because that is where I heard differences? Group delay and phase changes would be my guess and not normally tested. In my interconnect cable tests I found measurable differences in left channel peak levels (using music) of up to 0.4db; this ordered the 8 cables I used exactly by cost btw. None of your measurements are musically related but are electrically sound. We just need to create some new standardized measurements using musical wave forms I think.

There are no musical waveforms on USB cables; just different voltage potentials which represent a series of 1s and 0s. A USB cable either works (a 1 goes in and a 1 comes out) or it does not work (a 1 goes in and a 0 comes out) and when it does not work it typically results in an obvious failure, such as the sound cutting out completely. To have a capacity to shape the audio signal in such a way that one cable merely sounds more pleasing than another or one cable being slightly louder than another would require active processing on the cable which can decode the digital signal, manipulate the encoded data as desired, and then re-encode the data.

Have you thought about noise that is induced in such a cable and/or passed from the source to the receiver? Do you know what USB isolators do and why they might bring improvements to sound quality?Has the author of those measurements actually heard any differences between the 3 tested cables? Science usually comes second, after observations. Food for thought ;-)